NOTE: a StoredFieldVisitor implementation
should not try to load or visit other stored documents in
the same reader because the implementation of stored
fields for most codecs is not reeentrant and you will see
strange exceptions as a result.

needsField

Hook before processing a field.
Before a field is processed, this method is invoked so that
subclasses can return a StoredFieldVisitor.Status representing whether
they need that particular field or not, or to stop processing
entirely.